1. Field of the Invention
The present invention relates to method and apparatus for cutting a rubber strip at a predetermined longitudinal position and for shaping the upper surfaces of the trailing end of the rubber band member and the leading end of the remaining rubber strip to have a slope with a small angle relative to the general plane of the rubber strip or rubber band member,
2. Description of Related Art
Generally, tire production involves a process wherein an unvulcanized rubber strip, e.g., a long stretch of inner liner, is cut into rubber band members each having a predetermined length. Subsequently, the rubber member is wound around a shaping drum, with its leading end laid over the trailing end and adhered thereto. When such a rubber strip is cut into band members, both the leading end and the trailing end of the rubber member are shaped to have a slope in the thickness direction with a small angle relative to the general plane, in order to ensure that the rubber member has a thickness at the joint region, which is the same as the thickness at the remaining region of the rubber member, to thereby improve the product quality in terms of uniformity of tires.
As disclosed in U.S. Pat. No. 5,293,795, for example, it has been a conventional practice to use an anvil having a flat shaping surface to place the rubber strip thereon, in combination with a press cutter/shaper having a pair of inclined shaping surfaces on the front and tear sides. The inclined shaping surfaces of the cutter/shaper have a small inclination angle relative to the shaping surface of the anvil, and intersect each other forming a boundary therebetween. In this instance, after the rubber strip has been placed on the shaping surface of the anvil, the press cutter/shaper under a heated condition is advanced toward the anvil and brought into pressure contact with the rubber strip so as to cut it at a predetermined location within the region of the boundary between the front and rear shaping surfaces. Also, while the press cutter/shaper in pressure contact with the rubber strip is advanced toward the anvil, the trailing end of the rubber member and the leading end of the remaining rubber strip are progressively deformed and shaped by the inclined shaping surfaces of the cutter/shaper on the front and rear sides, respectively, to have a cross-section having a gradually reduced thickness and forming a relatively small angle with reference to the flat shaping surface of the anvil.
The conventional procedure as mentioned above proved to be generally effective for efficiently cutting and shaping a thin strip of unvulcanized rubber into rubber band members with a desired shape. However, it has been found that such procedure may not be applicable to particular types of rubber strip, such as a stretch of inner liner in which chafers with textile cords embedded therein are applied to, and along the side edges of the inner liner. This is because the textile cords embedded in the chafers impede cutting of the rubber strip, besides that the inclined shaping surfaces of the cutter/shaper are joined to each other at an obtuse intersection angle that is typically as large as about 170xc2x0 for the purpose of the desired shaping.
It is therefore an object of the present invention to provide a method and an apparatus, capable of readily cutting and shaping a rubber strip even when textile cords are embedded therein.
Briefly stated, according to the present invention, a rubber strip is cut and shaped into rubber band members by an apparatus which comprises an anvil having a flat shaping surface with an anvil groove that extends in the width direction of a rubber strip to be placed thereon, a press cutter/shaper arranged opposite to the anvil, a heating means for heating the press cutter/shaper to a predetermined temperature, and a moving means for moving the press cutter/shaper relative to the anvil. The press cutter/shaper comprises a pair of inclined shaping surfaces on front and rear sides, wherein these shaping surfaces of the press cutter/shaper are each inclined with a relatively small angle relative to the shaping surface of the anvil so as to intersect with each other at a predetermined intersection angle. The press cutter/shaper further comprises a cutting blade arranged between the front and rear shaping surfaces of the press cutter/shaper and protruding therefrom toward the anvil groove, wherein the cutting blade has a blade angle defined by front and rear surfaces of the cutting blade, which is smaller than the intersection angle of The shaping surfaces of the press cutter/shaper.
According to the present invention, a rubber strip to be cut and shaped into rubber band members is placed onto the anvil, and the press cutter/shaper heated to a predetermined temperature is then moved toward the anvil so that the cutting blade is forced into anvil groove while cutting the rubber strip at a predetermined cut position in its longitudinal direction to form a rubber band member. On this occasion, the trailing end of the rubber band member and the leading end of the remaining rubber strip are clamped between the front and rear shaping surfaces of the press cutter/shaper and the flat shaping surface of the anvil, respectively, and thereby progressively deformed and shaped to have a cross-section with a thickness which decreases gradually toward the cut position.
In the apparatus according to the present invention, in addition to a pair of inclined shaping surfaces, the press cutter/shaper comprises a cutting blade with a blade angle that is smaller than the intersection angle of the shaping surfaces of the press cutter/shaper. The cutting blade serves to positively cut the rubber strip into rubber members even when reinforcing cords are embedded in the rubber strip, while the inclined shaping surfaces serve to progressively deform and shape the trailing end of the rubber band member and the leading end of the remaining rubber strip, which are clamped between the front and rear shaping surfaces of the press cutter/shaper and the flat shaping surface of the anvil, respectively. Such a unique arrangement of the press cutter/shaper simultaneously allows for the cutting blade to have a blade angle suitable for cutting the rubber strip, and also for the inclined shaping surfaces to have an intersection angle that can be optimized primarily for the deformation and shaping of the trailing end of the rubber band member and the leading end of the remaining rubber strip.
It is preferred that at least one of the front surface and rear surface of the cutting blade is pressed against corresponding edge of the anvil groove so as to cut the rubber strip at a predetermined cut position. In this instance, it is possible to stably cut the rubber strip successively over a long period, since the edge of the cutting blade is effectively prevented from premature wear.
For achieving a more positive cutting of the rubber strip, it is preferred that both the front and rear surfaces of the cutting blade are pressed against respective edges of the anvil groove so as to cut the rubber strip at predetermined two sites.
When the cutting of the rubber strip is carried out at two sites as mentioned above, however, rubber scraps of the rubber strip are generated as a result of cutting, and such scraps tend to accumulate in the anvil groove. Unless removed or otherwise treated properly, the rubber scraps as being successively accumulated in the anvil groove often result in formation of undesirable solid mass that tends to adhere to the rubber strip or rubber band member. In order to effectively avoid possible accumulation of rubber scraps in the anvil groove, it is preferred that the anvil groove is V-shaped in cross-section, having a groove wall intersection angle between front and rear walls of the anvil groove, wherein the groove wall intersection angle is approximately same as the blade angle of the cutting blade.